This invention relates to a reversible, toggle operated, fluid driven tool such as a screwdriver having a "push to start"; torque controlled, fluid shut-off; and "release to reset" mechanism.
Fluid operated tools for driving fasteners and the like typically incorporate a rotary vane air motor to drive a rotary output shaft. Such tools are often equipped with a torque sensitive clutch mechanism. When a specific resistance to torque is sensed, the clutch mechanism automatically slips and terminates further tool driving force to the fastener.
Starting the tool is often effected by positioning a tool bit against the fastener and axially translating the bit by pushing it against the fastener. Axial translation of the bit operates a mechanism which opens a fluid supply valve to the tool. Such a tool is often referred to as a "push to start" controlled tool.
To combine start up control, torque control and automatic shut-off in a single tool is a desirable goal. In fact, many tools include torque responsive shut-off mechanisms sometimes coupled with a "push to start" mechanism for initiating operation of the tool.
It is also desirable to have all of the tool operations, including starting the tool, torque control and shut-off as well as resetting, associated merely with the activity of placing the tool against a fastener or removing the tool from a fastener, i.e. "push to start--release to reset". Various prior art references disclose devices of this general nature. Of particular pertinence is U.S. Pat. No. 4,576,270 issued Mar. 18, 1986 for a torque control and fluid shutoff mechanism for a fluid operated tool. That application and the references cited therein are incorporated herewith by reference.
U.S. Pat. No. 4,576,270 teaches the use of a bit which is axially translatable (push to start) in order to open the inlet valve to the tool for operation of a rotary vane air motor. A clutch mechanism in the tool comprises opposed, interlocking jaws which are associated with a bit holder and drive shaft respectively. Upon reaching a threshold torque, the jaws separate by rotating relative to one another thereby causing the drive shaft to disconnect from the bit holder and the inlet valve to close and terminate fluid flow to the rotary vane air motor. Subsequent release of the bit from the fastener resets the tool for further operation.
Such tools do not normally include a toggle operated or reversible trigger operated control switch because of the redundancy that results from a trigger control and push to start control. On the other hand, toggle or trigger operated tools may include a torque sensing or limiting feature. Toggle or trigger controlled tools are disclosed in U.S. Pat. Nos. 3,578,091; 3,710,873 and 3,741,313.
While the tools disclosed in the aforesaid patents are quite useful, an improved mechanism is desired having a simple, push to start operation, torque control, a reversible trigger or toggle switch control, and also having a reset capability associated with removal of the tool from a fastener. These are among the features and advantages which inspired the development of the present invention.